This proposed research is designed as a systematic investigation of several aspects of hormonal regulation of hepatic metabolism as studied in the isolated rat hepatocyte, with particular emphasis on the role of insulin. Studies will be undertaken to critically examine techniques of hapatocyte isolation necessary to generate hormone-responsive cells. Hormone responsiveness will be characterized by the study in this system of the regulation of glycogen synthesis and fatty acid biosynthesis. This characterized cell system will then be used to study the hormonal regulation of two other aspects of hepatic metabolism, free fatty acid metabolism and hepatic phosphopeptide metabolism. These studies will aid in the understanding of the hormonal regulation of hepatic metabolism in diabetes mellitus and in the states of hypertriglyceridemia and will provide a model for the study of hormone action in vitro.